D3083: Evaluating wheat genotypes with different stem solidity alleles for resistance to wheat stem sawfly (Cephus cinctus Norton)

The wheat stem sawfly (WSS, Cephus cinctus Norton) is a major insect pest of wheat in the Great Plains of North America and Canada, and its range is expanding. Host plant resistance using wheat lines with solid stems has been the primary means of managing WSS for several decades, as other management options are largely ineffective. Stem solidity is primarily controlled by genes at the quantitative trait locus Qss-msub.3BL on chromosome 3B, although there are other genes/alleles that impact stem solidity, and expression of stem solidity can change with plant growth stage. The objective of the study was to evaluate stem solidity levels and resistance to WSS of wheat genotypes with different stem solidity genes/alleles: 1) the rescue allele on chromosome 3B, 2) the Conan allele associated with “early solidity”- hexaploid 3B, 3) the Goldenball allele, fully solid-dosage allele on 3B, 4) the Pierce allele associated with “early solidity”- tetraploid 3A, and 5) susceptible hollow-stemmed checks. We conducted a no-choice greenhouse experiment using two levels of insect infestation: 1) not infested, 2) two sawfly females added to individually caged plants for 48 h. Half of the plants were destructively sampled shortly after oviposition to assess solidity and egg densities (non-preference), and the remaining plants were sampled at maturity to quantify stem solidity and WSS larvae (antibiosis). Experiments are ongoing, but preliminary results indicate changes in stem solidity over time depended on wheat line identity. Understanding solidity genes/alleles associated with consistent expression of stem solidity can help breeding efforts managing WSS.